The Tailfin racks seem to be the ultimate versions of modern racks. The carbon one gets down to 257g (~9oz), plus the weight of a dry bag and straps. I?m guessing that would be close to the weight of many seat bags. I myself have gone with a Revelate Spinelock, but I might consider a Tailfin in the future. Pricey, though.
https://www.tailfin.cc/product/pannier-racks/carbon-racks/carbon-rack/
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